Airblader commented on a change in pull request #460:
URL: https://github.com/apache/flink-web/pull/460#discussion_r690950672
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File path: _posts/2021-08-16-connector-table-sql-api-part1.md
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@@ -0,0 +1,234 @@
+---
+layout: post
+title: "Implementing a custom source connector for Table API and SQL - Part
One "
+date: 2021-08-18T00:00:00.000Z
+authors:
+- Ingo Buerk:
+ name: "Ingo Buerk"
+excerpt:
+---
+
+{% toc %}
+
+# Introduction
+
+Apache Flink is a data processing engine that keeps
[state](https://ci.apache.org/projects/flink/flink-docs-release-1.13/docs/ops/state/state_backends/)
locally in order to do computations but does not store data. This means that
it does not include its own fault-tolerant storage component by default and
relies on external systems to ingest and persist data. Connecting to external
data input (**sources**) and external data storage (**sinks**) is achieved with
interfaces called **connectors**.
+
+Since connectors are such important components, Flink ships with [connectors
for some popular
systems](https://ci.apache.org/projects/flink/flink-docs-release-1.13/docs/connectors/table/overview/).
But sometimes you may need to read in an uncommon data format and what Flink
provides is not enough. This is why Flink also provides [APIs](#) for building
custom connectors if you want to connect to a system that is not supported by
an existing connector.
+
+Once you have a source and a sink defined for Flink, you can use its
declarative APIs (in the form of the [Table API and
SQL](https://ci.apache.org/projects/flink/flink-docs-release-1.13/docs/dev/table/overview/))
to execute queries for data analysis without modification to the underlying
data.
+
+The **Table API** has the same operations as **SQL** but it extends and
improves SQL's functionality. It is named Table API because of its relational
functions on tables: how to obtain a table, how to output a table, and how to
perform query operation on the table.
+
+In this two-part tutorial, you will explore some of these APIs and concepts by
implementing your own custom source connector for reading in data from a
mailbox. You will use Flink to process an email inbox through the IMAP protocol
and sort them out by subject to a sink.
Review comment:
Having read the entirety now, we never actually achieved this goal? Did
I misunderstand the intention here?
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